In general, the resignation notice will indicate the filling time, when to officially resign and the reason. Of course, this reason is not necessarily a real reason, as long as it is a reasonable reason. The employer cannot refuse to accept the employee's resignation request because of insufficient reasons. This is just a notice to tell the employer that I am going to leave, so you can start recruiting people to replace me.
Self-resignation is a bad way and should only be implemented as a last resort. For example, a company does not abide by the labor law, forcing the company to fill in the so-called resignation application form, and the leader will not let it resign without approval. This is not standardized, so everyone has no choice but to leave. This method is not good, because when you go to another company, they will ask for the certificate of resignation, and quitting by yourself means that you can't get the certificate of resignation, and they will ask the last company about you.
Besides, ordinary regular companies will follow the labor law and will not force people to stay, so it is best to write the resignation notice in advance, hand over the work, and take the resignation certificate and leave after the expiration.